Electrical switch having a snap blade means and method of calibrating the same or the like

ABSTRACT

An electrical switch having a snap blade means of the overcenter variety that is confined in its movement to only the negative rate area thereof on one side of its over-center position and to a method for calibrating such an electrical switch by simple adjustments of an adjusting member engaging the snap blade means and an adjustable stop means that limits movement of the snap blade means relative to a fixed contact that cooperates with the blade means and is spaced from the stop means.

United States Patent Rosenberg et a1. [4 June 27, 1972 [5 ELECTRICALSWITCH HAVING A [561 References Cited SNAP BLADE MEANS AND METHOD OFUNITED STATES PATENTS CALIBRATING THE SANIE OR THE LIKE 3,395,375 7/1968Risk et al. .;.....337/347 X 3,239,633 3/ 1966 Bletz ..337/347Inventors: David g g; Siegfried R 2,879,357 3/1959 Them ..337/343 Mamke,both of lndlana County, 3,238,337 3/1966 Rosenberg et al. ...337/340[73] Assigneez Robmshaw Controls Company, 2,814,711 11/1957 Pliut ..337347 Richmond v 2,175,721 10/1939 Taylor ..337/345 [22] Filed Apr 19 19712,074,132 3/1937 Rich ..337/347 [2]] Appl. No.: 135,419 PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan RelatedUS. Application Data [60] Continuation Of Ser. N0. 714,992, March 21,1961, [57] ABSTRACT ti i a i 3 1, gg z 1 5 An electrical switch having asnap blade means of the overgg g i? g ggggg arc center variety that isconfined in its movement to only the negative rate area thereof on oneside of its over-center posi- 52] U S 337/347 29/622 337/94 tion and toa method for calibrating such an electrical switch 51 lm.c1..1111111111111113615' 176K1101h 37/12 110111 37 26 by Simpleadjusmems adjusting member engaging the 58 Field of Search ..337 340 343345 347 94- snap blade means and an adjustable means that limitsmovement of the snap blade means relative to a fixed contact thatcooperates with the blade means and is spaced from the stop means.

12 Claims, 13 Drawing figures PATENTEDJUNZ? I972 3, 673,535 SHEET 10F 3J D I '09 4 23 INVENTOK 23 98 DAVID MILTON ROSENBERG BY SIEGFRIED EMILMANECKE FIG-8 g, v 15 THEIR ATTORNEYS PATENTEDJUHZ? I972 3.673535 SHEETBN3 7 .FORCE 1o LEFT FORCE T0 m :20 I A D v i DEFLECTiON |2| DEFLECTIONTO RIGHT v v T0 LEFT v DEFLECTION= 1 I us To LEFT 8 n9 FIG?" y c, Q I||7 FORCE I v TO RIGHT l v I E ll2 ME ,9', 4 7 n4 7 H\ l FIG-I2INVENTORY DAVID MILTON ROSENBERG BYSIEGFRIED EMIL mmscxe THEIR ATTORNEYSELECTRICAL SWITCH HAVING A SNAP BLADE MEANS AND METHOD OF CALIBRATINGTHE SAME OR THE LIKE This application is a continuation of application,Ser. No. 714,992, filed Mar. 21, 1961, which, in turn, is a divisionalpatent application of its parent patent application, Ser. No. 300,468,filed Aug. 7, I963, which, in turn, is a Continuationin-part of thecopending patent application, Ser. No. 263,033, filed Mar. 5, 1963, andentitled Thennostat or the Like and Parts Therefor," now 0.8. Pat. No.3,238,337.

This invention relates to an improved thermostat or other control deviceas well as to an improved method for providing such a structure or thelike.

It is well known to provide a thermostat for controlling the operationof an electrical heater means for a water heater tank or the like, thethermostat including a bimetal member which senses the wall temperatureof the tank and controls an electrical switch or the like to selectivelyenergize and deenergize such heating means in accordance with thetemperature sensed. By properly selecting the initial position of thebimetal member, the thermostat is adapted to maintain the temperature ofthe water in the tank at a selected temperature.

Accordingly, it is an object of this invention to provide an improvedthermostat or the like of the above described type and which has one ormore of the novel features of this invention hereinafter described orillustrated.

Another object of this invention is to provide improved methods forproviding such a thermostat or the like.

Other objects, uses and advantages of this invention are apparent from areading of this description, which proceeds with reference to theaccompanying drawings forming a part thereof and wherein:

FIG. 1 is a perspective view of the improved thermostat of thisinvention.

FIG. 2 is a bottom view of the thermostat illustrated in FIG. 1 and hasthe rear cover thereof removed.

FIG. 3 is an axial cross-sectional view taken on line 3-3 of FIG. 2.

FIG. 4 is an enlarged fragmentary view of the temperature selectingmeans of the thermostat illustrated in FIG. 3.

FIG. 5 is a view similar to FIG. 3 and illustrates the thermostat inanother operating position thereof.

FIG. 6 is a cross-sectional view taken on line 6--6 of FIG. 3.

FIG. 7 is an enlarged cross-sectional view taken on line 7-7 of FIG. 3with the background structure removed.

FIG. 8 is a cross-sectional view taken on line 8-8 of FIG. 3.

FIG. 9 is a cross-sectional view taken on line 9-9 of FIG. 3.

FIG. 10 is a view similar to FIG. 3 and illustrates another embodimentof this invention.

FIG. 11 is a schematic graph illustrating the deflection and force of asnap spring as utilized according to the teachings of this invention.

FIG. 12 is a schematic graph illustrating the deflection and force of abimetal member as utilized according to the teachings of this invention.

FIG. I3 is a schematic graph illustrating the deflection and force ofthe snap spring and bimetal member when utilized together according tothe teachings of this invention.

While the various features of this invention are hereinafter describedand illustrated as being particularly adaptable to provide a waterheater tank thermostat or the like, it is to be understood that thevarious features of this invention can be utilized singly or in anycombination thereof to provide other control devices or the like.

Therefore, this invention is not to be limited to only the embodimentsillustrated in the drawings, because the drawings are merely utilized toillustrate one of the wide variety of uses of this invention.

Referring now to FIG. I, the improved thermostat or the like of thisinvention is generally indicated by the reference numeral and comprisesa substantially cup-shaped housing 21 formed of suitable insulatingmaterial or the like and having the rear or open end thereof closed by arear cover plate 22 formed of metal or the like.

The housing 21 is provided with a plurality of input and output terminalposts 23 for respectively interconnecting the thermostat 20 to a powersource and to the heater means or other electrical devices of a waterheater tank or. the like, the terminal posts 23 comprising conventionalthreaded screwlike members.

The thermostat 20 is so constructed and arranged in a manner hereinafierdescribed that the same is adapted to automatically maintain thetemperature of the water in a water heater tank at a temperatureselected by the manual setting of a rotatable indicating knob 24 carriedby the housing 21 in a manner hereinafter described, whereby the pointer25 of the knob 24 will indicate proper temperature setting as providedby the scale 26 carried on a plate 27 secured to the housing 21 in anysuitable manner.

The particular details of the thermostat 20 will now be described andreference is made to FIGS. 2 and 3 wherein a substantially flat bimetalmember 28 is disposed in the cavity 29 of the housing 21 and has opposedends 30 and 31.

The end 30 of the bimetal member 28 is secured by rivets 32 or the liketo the middle leg 33 of a plural leg member 34 having its outer legs 35and 36 respectively secured to the housing 21 by rivets 37 and 38 or thelike. The middle leg 33 of the plural leg member 34 forms a leafspring-like member that normally tends to move downwardly toward thehousing 21 in FIG. 3 and carry the end 30 of the bimetal member 28therewith.

A calibration screw plate 39 is disposed in the housing 21 below theplural leg member 34 and is secured to the housing 21 by the previouslydescribed rivets 37 and 38, the calibration screw plate 39 having athreaded aperture 40 passing substantially centrally therethrough andhaving an end flange 41 projecting outwardly beyond the wall 42 of thehousing 21.

A calibration screw or externally threaded adjusting member 43 passesthrough aligned apertures 44 and 45 in the plate 27 and housing 21 to bethreadedly received in the threaded aperture 40 of the calibration screwplate 39 as illustrated in FIG. 3, whereby the free end 46 of thecalibration screw 43 engages the middle leg 33 to limit movement thereoftoward the housing 21.

The selector knob 24 is press fitted on a knurled portion 47 of thecalibration screw 43 at a point outside the housing 21, whereby theindicating pointer 25 thereof is adapted to be moved across the dialface 26 in unison with rotation of the calibration screw 43, thecalibration screw 43 being adapted to be rotated relative to the housing21 by inserting a screw driver or the like in the bifurcated end 48thereof.

In this manner, the end 30 of the bimetal member 28 is adapted to beraised and lowered in FIG. 3 by movement of the calibration screw 43 inand out of the housing 21, whereby as the end 30 of the bimetal member28 is moved upwardly a higher temperature setting is provided for thethermostat 20. Conversely, downward movement of the end 30 of thebimetal member 28 in FIG. 3 provides a lower temperature setting for thethermostat 20.

A movable motion transmitting member or tie bar 49 is disposed in thehousing 21 and is formed of suitable insulating material or the like,the member 49 having a plurality of slot means 50, 51, and 52 passingtherethrough in the manner illustrated in FIG. 7. The slot means 50 ofthe member 49 is defined in part by opposed surface means 53 and 54,which are substantially straight and parallel to each other while theslot means 51 is defined between opposed surfaces 55 and 56 respectivelydefining substantially triangular portions having the apexes 57 and 58thereof facing each other and disposed apart a desired distance for apurpose hereinafter described. The slot means 52 of the member 49 isdefined between opposed surface means 59 and 60, the opposed surface 59defining a substantially triangular portion having an apex 61 disposedsubstantially intermediate the spaced straight portions of the opposedsurface means 60. The portions 62 of the member 49 are separated fromeach other by a recess 63 which intersects the slot means 52 for apurpose hereinafter described.

The movable end 31 of the bimetal member 28 is operativelyinterconnected to the member 49 to cause vertical movement of the member49 in FIG. 3 and, thus, to control the operation of a pair of electricalswitches 64 and 65 disposed in the housing 21.

In particular, the movable end 31 of the bimetal member 28 is dividedinto three legs 66, 67, and 68, with the middle leg 67 being bent out ofthe plane of the outer legs 66 and 68. In this manner, the legs 66-68 ofthe free end 31 of the bimetal member 28 can be press fitted through theslot means 50 of the member 49, whereby the legs 66-68 are placed undercompression between the opposed surfaces 53 and 54 of the slot means50in the manner illustrated in FIG. 7.

This press fit interconnection of the free end 31 of the bimetal member28 to the member 49 prevents any lost motion between the free end 31 ofthe bimetal member 28 and the lever 49.

The free end 69 of the middle leg 67 of the bimetal member 29 can bebent transversely in the manner illustrated in FIG. 3 to prevent themember 49 from moving to the right relative to the bimetal member 28while movement of the member 49 to the left relative to the bimetalmember 28 is prevented by shoulders 70 of the bimetal member 28.

The electrical switch 64 comprises a fixed contact 71 and a cooperableand movable contact 72, the fixed contact 71 being carried on aconductive plate 73 secured to a post 74 of the housing 21 by aconductive rivet 75 interconnected to one of the terminal posts 23.

The movable contact 72 is carried by a resilient switch blade 76 havingone end 77 thereof secured to a post 78 of the housing 21 by aconductive rivet 79 interconnected to one of the terminal posts 23. Theother end 80 of the resilient switch blade 76 passes through the slotmeans 51 of the member 49 and is normally biased against the apex 57 ofthe surface means 55 of the member 49, regardless of the position of themember 49 relative to the housing 21.

As illustrated in FIG. 7, the end 80 of the switch blade 76, whendisposed against the apex 57 of the surface means 55 of the member 49,is normally spaced from the apex 58 of the surface means 56 thereof adistance of approximately 0.012 of an inch for a purpose hereinafterdescribed.

Thus, it can be seen that when the movable end 31 of the bimetal member28 moves downwardly from the position illustrated in FIG. 3 to theposition illustrated in FIG. upon the bimetal member 28 sensing anincrease in temperature value, the member 49 causes the movable contact72 to move into electrical contact with the fixed contact 71.

The electrical switch 65 comprises a fixed contact 81 and a movablecontact 82 cooperable with the fixed contact 81, the fixed contact 81being carried on a conductive plate 113 secured to a post 83 of thehousing 21 by a conductive rivet 84 interconnected to one of thetenninal posts 23.

The movable contact 82 is carried by a switch blade 85 having one end 86thereof secured to a conductive plate 87 by rivets 88 or the like, theconductive plate 87 being secured to a post 89 of the housing 21 by aconductive rivet 90 interconnected to one of the tenninal posts 23 inthe manner illustrated in FIG. 8.

The other end 91 of the switch blade 85 passes through the slot means 52of the member 49 in such a manner that the end 91 of the switch blade 85is compressed between the opposed surface means 59 and 60 of the member49 to prevent any lost motion between the member 49 and the switch blade85.

For example, reference is made to FIG. 7 wherein it can be seen that theportions 61 and 62 of the slot means 52 are so constructed and arrangedthat the same slightly bow the switch blade 85 as the switch blade 85passes through the slot means 52 to place the same under compression inthe slot means 52 and, thereby, prevent any lost motion between theswitch blade 85 and the member 49.

A leg 92 extends outwardly from the end 91 of the switch blade 85 and isbent transversely relative thereto to prevent outward movement of thelever 49 relative to the switch blade 85.

As illustrated in FIG. 9, the switch blade is divided into three legs93, 94 and 95 intermediate its ends 86 and 91. The outer legs 93 and 95are suitably crimped at 96 in the manner illustrated in FIGS. 3 and 9 toplace the middle leg 94 under compression whereby the switch blade 85 isrendered snapacting for a purpose hereinafter described.

A leaf spring 97 is disposed in the housing 21 and has one end 98thereof secured to the conductive plate 87 by the same rivets 88 thatsecure the switch blade 85 to the conductive plate 87.

The leaf spring 97 is interconnected to the middle leg 94 of the switchblade 85 by a rivet 99 and normally tends to move downwardly toward thehousing 21 in the manner illustrated in FIG. 3 to aid the snap-actingfunction of the switch blade 85.

The free end 100 of the leaf spring 97 is engaged by a threadedadjusting member 101 threadedly disposed in an internally threaded bore102 formed in the housing 21, the adjusting member 101 being adapted tolimit downward movement of the leaf spring 97 in FIG. 3 to provide ameans for establishing the desired snap point of the switch blade 85.

Therefore, it can be seen that as the movable end 31 of the bimetalmember 28 tends to move downwardly in FIG. 3 upon an increase in sensedtemperature value, the member 49 also tends to move downwardly therewithand imposes a downward force on the switch blade 85. When a sufficientdownward force is imposed on the switch blade 85 by the member 49, theswitch blade 85 snaps downwardly in the manner illustrated in FIG. 5whereby the electrical contact between the contacts 81 and 82 isabruptly terminated while the contacts 72 and 71 are brought intoelectrical contact with each other.

Conversely, when the movable end 31 of the bimetal member 28 tends tomove upwardly upon a decrease in sensed temperature value, the switchblade 85 subsequently snaps upwardly when a sufficient force has beenapplied thereto by the member 49 tending to pull the same upwardlywhereby the contact 82 is snapped into electrical engagement with thecontact 81 while the contacts 72 and 71 are snapped open in the mannerillustrated in FIG. 3.

The rear cover 22 of the thermostat 20 is substantially cupshaped totelescopically receive the rear of the housing 21 in the mannerillustrated in FIG. 3, the housing 21 having a pair of opposed recesses103 formed therein and terminating in shoulders 104 as illustrated inFIG. 1.

The rear cover 22 has a pair of inwardly biased tangs 105 which areadapted to snap into the recesses 103 when the cover 22 and housing 21are telescoped together whereby the ends of the tangs 105 of the cover22 catch against the shoulders 104 to secure the cover 22 to the housing21.

In addition, the cover 22 has a slot 106 passing therethrough to snapfittingly receive the flange 41 of the calibration screw plate 39 in themanner illustrated in FIGS. 1 and 3 whereby not only does thecalibration screw plate 39 provide an anchor for the back cover 22, butalso the calibration screw plate 39 acts as a conductor to pick up andtransfer surface temperature to the bimetal member 28.

If desired, the cover 22 can have a pair of outwardly directed ears orlugs 107 in the manner illustrated in FIG. 1 whereby the thermostat 20can be secured to the desired surface by suitable fastening memberspassing through apertures 108 in the lugs 107.

Altemately, or additionally, the back cover 22 can be provided with ears109, FIG. 1, which provide means for mounting the thermostat 20 to asuitable appliance by the use of spring brackets which snap down on theears 109 at the points 1 10.

The operation of the thermostat 20 of this invention will now bedescribed.

After the thermostat 20 has been mounted to the water heater tank or thelike and the power source lines and heater means or other electricaldevices have been appropriately interconnected to the terminal posts 23thereof, the operator sets the pointer 25 to the desired temperature,such as F.

as illustrated in FIG. 1 whereby the end 46 of the calibration screw 43properly positions the end 30 of the bimetal member 28 relative to thehousing 21.

Assuming that the temperature being sensed by the bimetal member 28 isbelow the temperature that would cause the thermostat 20 to turn off theheater means of the water heater tank, the switches 64 and 65 aredisposed in the position illustrated in FIG. 3 whereby suitableelectrical current is directed to the heater means of the water heatertank.

However, as the temperature of the water in the water heater tankincreases to the selected temperature, the movable end 31 of the bimetalmember 28 tends to move downwardly .from the position illustrated inFIG. 3 until the same exerts sufficient downward force on the member 49to cause the switch blade 85 to snap downwardly to the positionillustrated in FIG. 5 whereby the contacts 81 and 82 are snapped openwhile the contacts 72 and 71 are snapped closed so that the heatingmeans for the water heater tank is de-energized as the temperature ofthe water in the tank is at the selected temperature value.

With the thermostat 20 disposed in the position illustrated in FIG. 5and the temperature of the water in the water tank decreasing below theselected temperature, the end 31 of the bimetal member 28 tends to moveupwardly from the position illustrated in FIG. 5 until the same exertssufficient force to cause the switch blade 85 to snap in an upwarddirection to snap close the contacts 81 and 82 and to snap open thecontacts 71 and 72 to again energize the heating means of the waterheater tank.

During this last operation, it may be that the contacts 71 and 72 hadbecome stuck in their closed position while the member 49 is beingsnapped upwardly. However, it can be seen from FIG. 7 that the member 49can move relative to the switch blade 76 before the apex 58 of the lowersurface means 56 thereof comes into contact with the switch blade 76whereby the member 49 can apply a hammer blow to the switch blade 76 tounstick the contacts 71 and 72 should the same become stuck duringoperation of the thermostat 20.

Thus, it can be seen that the thermostat 20 can cycle in such a mannerto maintain thetemperature value of the water in the water heater tankat the selected temperature value.

Therefore, it can be seen that an improved thermostat or the like isprovided by this invention as well as improved parts for such athermostat or the like.

While the thennostat 20 previously described has been illustrated as asingle pole double throw unit, it is to be understood that the same canbe constructed in a like manner to form a single pole single throw unitby simply eliminating the fixed contact 71 and switch blade 78 in themanner illustrated in FIG. 10 whereby another thermostat of thisinvention is generally indicated by the reference numeral 111 and partsthereof similar to the thermostat previously described or indicated bylike reference numerals followed by the reference letter a.

As illustrated in FIG. 10, the fixed contact 71 and switch blade 76 havebeen eliminated whereby the member 490 merely controls the operation ofthe electrical switch 65a in the manner previously described.

However, when the member 49 of the thermostat 20 was snapped downwardlyfrom the position illustrated in FIG. 3 to the position illustrated inFIG. 5, the engagement between the contacts 71 and 72 thereof limitedthe downward movement of the member 49 upon the snap action of theswitch blade 85.

Therefore, in order to limit the downward movement of the member 49a ofthe thermostat 111 illustrated in FIG. 10, an adjusting screw 112 isadjustably carried by the housing 21a to limit downward movement of themember 49a after the contacts 81a and 82a have been snapped open in themanner previously described, the adjusting screw 112 being engageable bythe end of the member 49a.

Therefore, it can be seen that the thermostat of this invention can bemodified in any desired manner while still performing the desiredfunctions of this invention.

The particular details of the operation of the snap switch blades orsprings and 85a in combination with the bimetal members 28 and 28a willnow be described and reference is made to FIGS. 1 1-13.

As illustrated in FIG. 11, the snap spring blade 85a or 85 isillustrated in full lines in its most leftward position and in dottedlines in its most rightward position after it has snapped over center,the over center position being illustrated by the vertical line 114.Such movement of the snap spring blade 85:: is represented by thehorizontal line whereby point 0 on line 115 is the dead center positionof snap spring blade 85 and points A and D on line 115 are the extremepositions of deflection of the snap spring blade 85:: from its centerposition 0.

A curve 116 is plotted on the lines 114 and 115 and represents the forceprovided by the snap spring blade 85a in any of its deflected positions,the curve 1 16 being very similar to a sine wave curve.

Thus, it can be seen the snap spring blade 85a or 85 has no forcetending to move the same in a particular direction when the blade 85a or85 is disposed at positions A, O and D.

However, as the snap spring blade 85a or 85 is deflected from point A topoint B, the snap spring blade has an increasing force tending to moveitself back to the left to point A. Similarly, as the snap spring blade85a or 85 is deflected from point 0 to point C, the blade has anincreasing force tending to move itself back to the right to point D.

This force of the snap spring blade 850 or 85 between points, A, B andD, C is known as the positive rate range of the snap spring blade.

However, as the snap spring blade 85a or 85 is deflected from point Btoward point 0 or from point C toward point 0, the opposing force of thesnap spring blade decreases whereby movement of the blade between thepoints B, 0 and C, O is known as the negative rate range of the snapspring blade.

The thermostats of this invention utilize the negative rate range of thesnap spring blade 85a or 85 in a manner now to be described.

As illustrated in FIG. 1, the fixed contact 81a or 81 is so constructedand arranged that the same limits the movement of the snap spring blade850 or 85 to the left at point E on the curve 116.

Similarly, the adjustable stop means 112 of FIG. 10 or the contact 71 ofFIG. 5 is so constructed and arranged that the same limits movement ofthe snap spring blade 85a or 85 to the right at point F on the curve 116.

Thus, it can be seen that the movement of the snap spring blade 8511 or85 is limited between the points E and F on the curve 116 by the fixedcontact and stop means so that the entire range of movement of the snapspring blade 850 or 85 is the negative rate range thereof and neversnaps over center.

The use of the change in force of the snap spring blade 85a or 85between points E and F will later be described.

Reference is now made to FIG. 12 wherein the vertical line 117represents the bimetal member 280 or 28 at rest and the horizontal line118 represents deflection of the bimetal member 28a or 28 to the left.

Thus, as the bimetal member 28a or 28 is deflected to the left from itsat rest point 119 to point 120, the bimetal member exerts an increasingforce tending to move the bimetal member back to position 119, the forcebeing represented by the substantially straight line 121.

By combining the deflection force curve of the snap spring blade 85a or85 with the deflection force curve of the bimetal member 280 or 28, itcan be seen that the contact carried by the snap spring blade 85a or 85can be substantially snapped between its closed and opened positionswithout requiring the snap spring blade 85a or 85 to be snapped overcenter.

For example, reference is now made to FIG. 13 wherein the action of thethermostats of this invention is graphically illustrated.

As illustrated in FIG. 13, point E represents the contact closedposition of the movable snap spring blade contact 82a or 82 and point Prepresents the contact open position thereof whereby it can be seen thatthe snap spring blade 85a or 85 never reaches its dead center position0.

Without any bimetal efiect, the contacts 820, 81a or 82, 81 will beclosed with the amount of pressure indicated at point E.

As the temperature increases, the bimetal member 28a or 28 will startbuilding up force in opposition to the snap spring blade force. When thetemperature sufficiently increases so that the bimetal force equals orjust exceeds the snap spring force, the contacts 824, 81a or 82, 81 willopen a slight amount and the snap spring force will be reduced. Thebimetal force will also be reduced but not as much as the snap springforce and, consequently, the bimetal member 28a or 28 will continue toopen the contacts 82a, 81a or 82, 81 until the contact 82a or 82 hits,in effect, the stop means 1 12 or 71.

At this point the snap spring force will have been reduced along line EFto point F. The bimetal force will have reduced along line EG to pointG. Since, at this time, the bimetal force is greater than the snapspring force, the bimetal will push the snap spring, in effect, againstthe stop means.

Since the contacts 82, 81a or 82, 81 are now in the opened position atpoint F, the temperature will begin to drop. As the temperature drops,the bimetal force will be reduced along line GF.

When the bimetal force reduces to point F or slightly less, the snapspring force will start to move the contact 82a or 82 away from its stopmeans. As it moves away, the snap spring force increases at a greaterrate than the bimetal force, and it thus closes the contacts 820, 81a or82, 81 with a snap action.

The snap force changes from point F to point E while the bimetal forcechanges from point F to point H.

The contacts 82a, 810 or 82, 81 are now closed and the temperature willagain start to rise. As the temperature rises, the bimetal force willincrease along line HE.

When the bimetal force reaches point E, the contacts 82a, 810 or 82, 81will snap open and the cycle will be repeated in the above manner.

Thus, it can be seen that the thermostats of this invention only utilizethe negative rate range of a snap spring to provide a snap actionmovement of a movable contact between its opened and closed positions.

The calibration procedure utilized to obtain the abovedescribed snapaction for the thermostat 111 of FIG. 10 is as follows:

1. Only the parts 21a, 85a, 49a, 112, 65a, and 101a are assembledtogether as illustrated in FIG. 10.

2. The screw 101a is turned inward until the snap spring blade 85a snapsdownward.

3. The screw 112 is then turned inward until contacts 820 and 81a justmake contact. This position can be detected with a continuity testerconnected to the rivet 90 and the rivet 84.

4. The screw 112 is then turned out about one-half turn to provide avery slight gap such as ten thousandths of an inch.

5. The screw 10111 is then turned out until the snap spring blade 85asnaps to close contacts 820 and 81a.

The calibration procedure utilized to obtain the abovedescribed snapaction for the thermostat of FIG. 3 is as follows:

1. Only the parts 21, 101, 85, 81, 49, 71, 72, 76, and 79 are assembledtogether in the manner illustrated in FIG. 3.

2. The screw 101 is then turned inward until the switch blade 85 snapsdownward.

3. The support for contact 71 is then adjusted to provide a slight gapbetween contacts 81 and 82.

4. The screw 101 is then turned out until the snap spring 85 snaps toclose contacts 81 and 82.

Therefore, it can be seen that it is a relatively simple procedure toprovide the above calibration for the thermostats 20 and 1 11 in orderto have the snap action previously described.

What is claimed is:

1. In a method for making an electrical switch having a movable snapspring blade means of the over-center variety provided with an end thatcooperates with a pair of spaced stop means to limit movement of saidend of said snap blade means, the improvement comprising the steps ofadjusting an adjusting member of said switch to cause said snap springblade means to move said end away from one of said stop.

means, adjusting the other stop means for said snap spring blade meansto hold said end of said snap spring blade means slightly spaced fromsaid one stop means, thereafter adjusting said adjusting member to causesaid snap spring blade means to move said end toward said one stop meansand place said end thereof against said one stop means wherebysubsequent movement of said end of said snap spring blade means aslimited by said stop means will only be on one side of the overcenterposition of said snap spring blade means, and, thereafter, operativelyassociating a bimetal member with said snap spring blade means to causemovement of said snap spring blade means between said stop means inrelation to temperature sensing condition of said bimetal member.

2. In a method as set forth in claim 1, the further improvement whereinsaid adjusting steps cause said subsequent movement of said end of saidsnap spring blade means to be in only the negative rate area of saidsnap spring blade means on said one side of the over-center positionthereof.

3. In a method as set forth in claim 1, the further improvement ofincluding the step of forming said one stop means from an electricalcontact and providing an electrical contact on said end of said blademeans to cooperate therewith.

4. In a method as set forth in claim 3, the further improvement ofincluding the step of adjusting said other stop means to move saidcontact carrying end of said blade means into electrical contact withsaid stop means contact after said first adjusting step and before saidsecond adjusting step.

5. In a method as set forth in claim 4, the further improvement ofincluding the step of testing the electrical contact between saidcontacts after the step of adjusting said other stop means to place saidblade means contact into contact with said stop means contact.

6. In a method as set forth in claim 1, the further improvement ofincluding the step of interconnecting a movable blade to said snap blademeans, said movable blade engaging said other stop means when said endof snap blade means is subsequently moved away from said one stop means.

7. In a method as set forth in claim 6, the further improvement ofincluding the step of forming said one stop means from an electricalcontact and providing an electrical contact on said end of said blademeans to cooperate therewith.

8. In a method as set forth in claim 7, the further improve ment ofincluding the step of forming said other stop means from an electricalcontact and providing an electrical contact on said blade to cooperatetherewith.

9. In a method for making an electrical switch having a movable snapspring blade means of the over-center variety provided with a contactcarrying en'd movable between a fixed contact and an adjustable stopmeans spaced from said fixed contact and having an adjusting memberengaging an intermediate portion of said blade means, the improvementcomprising the steps of adjusting said adjusting member in a directiontoward said snap blade means until it causes said snap blade means tosnap away from said fixed contact and against said stop means, adjustingsaid stop means toward said fixed contact to cause said blade meanscontact to just make contact with said fixed contact, thereafter,adjusting said stop means away from said fixed contact to provide aslight gap between said fixed contact and said blade means contact, thenadjusting said adjusting member in a direction away from said blademeans until said blade means snaps its contact against said fixedcontact, and, thereafter, operatively associating a bimetal member withsaid snap blade means to cause movement of said snap blade means betweensaid positions thereof in relation to temperature sensing conditions ofsaid bimetal member.

10. In a method as set forth in claim 9, the further improvement whereinsaid steps cause said snap blade means to move between said fixedcontact and said stop means in only the negative rate area of said snapblade means on one side of the over-center position thereof.

11-. In a method for making an electrical switch having a movable snapspring blade means of the over-center variety provided with a contactcarrying end movable relative to a first fixed contact and having anadjusting member engaging an intermediate portion of said blade means,said blade means being interconnected to a blade provided with a contactcarrying end movable relative to an adjustable fixed contact, theimprovement comprising the steps of adjusting said adjusting member in adirection toward said blade means until it causes said blade means tosnap away from said first fixed contact and move said contact of saidblade against said second fixed contact, adjusting said second fixedcontact to provide a slight gap between said first fixed contact andsaid contact of said blade means, thereafier, adjusting said adjustingmember in a direction away from said blade means until said blade meanssnaps said contact thereof against said first fixed contact, and,thereafter, operatively associating a bimetal member with said snapblade means to cause movement of said snap blade means between saidpositions thereof in relation to temperature sensing conditions of saidbimetal member.

12. In a method as set forth in claim 11, the further improvementwherein said steps cause said snap blade means to move relative to saidfirst fixed contact in only the negative rate area of said snap blademeans on one side of the overcenter position thereof.

I! i R i

1. In a method for making an electrical switch having a movable snapspring blade means of the over-center variety provided with an end thatcooperates with a pair of spaced stop means to limit movement of saidend of said snap blade means, the improvement comprising the steps ofadjusting an adjusting member of said switch to cause said snap springblade means to move said end away from one of said stop means, adjustingthe other stop means for said snap spring blade means to hold said endof said snap spring blade means slightly spaced from said one stopmeans, thereafter adjusting said adjusting member to cause said snapspring blade means to move said end toward said one stop means and placesaid end thereof against said one stop means whereby subsequent movementof said end of said snap spring blade means as limited by said stopmeans will only be on one side of the over-center position of said snapspring blade means, and, thereafter, operatively associating a bimetalmember with said snap spring blade means to cause movement of said snapspring blade means between said stop means in relation to temperaturesensing condition of said bimetal member.
 2. In a method as set forth inclaim 1, the further improvement wherein said adjusting steps cause saidsubsequent movement of said end of said snap spring blade means to be inonly the negative rate area of said snap spring blade means on said oneside of the over-center position thereof.
 3. In a method as set forth inclaim 1, the further improvement of including the step of forming saidone stop means from an electrical contact and providing an electricalcontact on said end of said blade means to cooperate therewith.
 4. In amethod as set forth in claim 3, the further improvement of including tHestep of adjusting said other stop means to move said contact carryingend of said blade means into electrical contact with said stop meanscontact after said first adjusting step and before said second adjustingstep.
 5. In a method as set forth in claim 4, the further improvement ofincluding the step of testing the electrical contact between saidcontacts after the step of adjusting said other stop means to place saidblade means contact into contact with said stop means contact.
 6. In amethod as set forth in claim 1, the further improvement of including thestep of interconnecting a movable blade to said snap blade means, saidmovable blade engaging said other stop means when said end of snap blademeans is subsequently moved away from said one stop means.
 7. In amethod as set forth in claim 6, the further improvement of including thestep of forming said one stop means from an electrical contact andproviding an electrical contact on said end of said blade means tocooperate therewith.
 8. In a method as set forth in claim 7, the furtherimprovement of including the step of forming said other stop means froman electrical contact and providing an electrical contact on said bladeto cooperate therewith.
 9. In a method for making an electrical switchhaving a movable snap spring blade means of the over-center varietyprovided with a contact carrying end movable between a fixed contact andan adjustable stop means spaced from said fixed contact and having anadjusting member engaging an intermediate portion of said blade means,the improvement comprising the steps of adjusting said adjusting memberin a direction toward said snap blade means until it causes said snapblade means to snap away from said fixed contact and against said stopmeans, adjusting said stop means toward said fixed contact to cause saidblade means contact to just make contact with said fixed contact,thereafter, adjusting said stop means away from said fixed contact toprovide a slight gap between said fixed contact and said blade meanscontact, then adjusting said adjusting member in a direction away fromsaid blade means until said blade means snaps its contact against saidfixed contact, and, thereafter, operatively associating a bimetal memberwith said snap blade means to cause movement of said snap blade meansbetween said positions thereof in relation to temperature sensingconditions of said bimetal member.
 10. In a method as set forth in claim9, the further improvement wherein said steps cause said snap blademeans to move between said fixed contact and said stop means in only thenegative rate area of said snap blade means on one side of theover-center position thereof.
 11. In a method for making an electricalswitch having a movable snap spring blade means of the over-centervariety provided with a contact carrying end movable relative to a firstfixed contact and having an adjusting member engaging an intermediateportion of said blade means, said blade means being interconnected to ablade provided with a contact carrying end movable relative to anadjustable fixed contact, the improvement comprising the steps ofadjusting said adjusting member in a direction toward said blade meansuntil it causes said blade means to snap away from said first fixedcontact and move said contact of said blade against said second fixedcontact, adjusting said second fixed contact to provide a slight gapbetween said first fixed contact and said contact of said blade means,thereafter, adjusting said adjusting member in a direction away fromsaid blade means until said blade means snaps said contact thereofagainst said first fixed contact, and, thereafter, operativelyassociating a bimetal member with said snap blade means to causemovement of said snap blade means between said positions thereof inrelation to temperature sensing conditions of said bimetal member. 12.In a method as set forth in claim 11, the further improvement whereinsaid steps cause said snap blade means to move Relative to said firstfixed contact in only the negative rate area of said snap blade means onone side of the over-center position thereof.